NPOI设置单元格背景色

NPOI设置单元格背景色在网上有好多例子都是设置为NPOI内置的颜色值

但是想用rgb值来设置背景色，即：通过HSSFPalette类获取颜色值时会抛出异常：Could not Find free color index

比如：http://www.cnblogs.com/yxhblog/p/6225018.html

最后找到 这个实现后才知道需要额外设置一步

http://www.cnblogs.com/huxiaolin/p/4813518.html

简化后代码如下：

private void button1_Click(object sender, EventArgs e)
        {
            //创建Excel文件的对象
            var book = new HSSFWorkbook();
            //添加一个sheet
            var sheet1 = book.CreateSheet("Sheet1");
            //给sheet1添加第一行的头部标题
            var row1 = sheet1.CreateRow(0);
            var s = book.CreateCellStyle();
            s.FillForegroundColor = GetColourByRGB(book, 82, 238, 172);
            s.FillPattern = FillPattern.SolidForeground;

            for (int i = 0; i < 10; i++)
            {
                row1.CreateCell(i).SetCellValue(i);
                row1.GetCell(i).CellStyle = s;
            }

            using (SaveFileDialog sf = new SaveFileDialog())
            {
                sf.Filter = "表格|*.xls";
                sf.AddExtension = true;
                if (sf.ShowDialog() == DialogResult.OK)
                {
                    //创建一个文档流对象
                    using (FileStream fs = new FileStream(sf.FileName, FileMode.Create))
                    {
                        //将内存里面的文档对象，写入到一个文档流中
                        book.Write(fs);
                    }
                }
            }
        }

        private short GetColourByRGB(HSSFWorkbook workbook, byte r, byte g, byte b)
        {
            var palette = workbook.GetCustomPalette();
            var hssfColor = palette.FindColor(r, g, b);
            if (hssfColor == null)
            {
                palette.SetColorAtIndex(HSSFColor.Lavender.Index, r, g, b);
                hssfColor = palette.GetColor(HSSFColor.Lavender.Index);
            }
            if (hssfColor != null)
            {
                return hssfColor.Indexed;
            }
            else
            {
                return short.MinValue;
            }
        }